High surface area zirconia

ABSTRACT

The invention relates to a high surface area zirconia, having a surface area of above 125 m 2  /g and preferably of above 200 m 2  /g after calcination. The high surface area zirconia product of the invention can be prepared by mixing a zirconium salt solution with an alkali or ammonium compound, the zirconium hydroxide precipitate being aged in the presence of an oxygen acid of an element of group 5 or 6 of the Periodic Table of Elements and subsequently being calcined, optionally after a washing step. The preferred acid is phosphoric acid.

FIELD OF THE INVENTION

The invention relates to high surface area zirconia, to a process forproducing such high surface area zirconia and to a process for theproduction of hydrocarbons from synthesis gas using high surface areazirconia.

BACKGROUND OF THE INVENTION

A process for the preparation of zirconia is known from French PatentNo. 2,590,887 teaching the use of an additive to obtain a relativelyhigh surface area zirconia, that still has a relatively high surfacearea after sintering, i.e., in the state wherein it is to be used as acatalyst or catalyst support. The additives used to this purpose are theoxides of silicon, rare earth metals and aluminum. The additives areused in an amount of about 1 to 10%, preferably 2 to 5%. A simple mixingprocess resulting into an intimate mixture of the zirconia and theoxides suffices. A coprecipitation of a zirconium oxide precursor withthe precursors of the further elements mentioned, is also suitable. Thepreferred method is the impregnation of zirconium oxide with a solutionof at least one salt precursor of the further oxides. The highestspecific surface area reached (m² /g) is 90 of a treatment at 400° C.Treatments at a higher temperature result into lower specific surfaceareas. One of the examples is a comparison and uses no additives. Thespecific surface area reached is 80 m² /g after a heat treatment at 400°C. and 20 m² /g after a heat treatment at 900° C. (The treatment takes 6hours).

U.S. Pat. No. 4,440,875 teaches a process for the production ofhydrocarbons from synthesis gas wherein a catalyst consisting ofzirconium oxide promoted with at least one alkali metal compound isused. Preferably the zirconium oxide has a specific surface area in therange from 20 to 500 m² /g and is the alkali metal compound a potassiumcompound. The only example, however, describes just a specific surfacearea of 122 m² /g resulting from a previous calcination step carried outin air for 2 hours at 450° C. The catalyst is obtained by dissolvingzirconium oxychloride in water and gradually adding ammonia to thesolution until the pH value of the solution is in the range from 7 to10. The precipitated zirconium hydroxide is separated from the solutionby filtration and washed. The filtration residue is subsequentlycalcined from 1 to 24 hours in the air at a temperature in the range offrom 300° C. to 1000° C.

The addition of an alkali metal compound to the catalyst improves theselectivity for butene.

The Journal of Physic. Chem. Institute 24-06-85 of the Soviet Unionteaches the production of zirconium dioxide with a high specific surfacearea by treating a solution of zirconium nitrate with ammonia andwashing the obtained gel, separating and drying it. It is then heatedfor 2 to 10 hours at 150° C. to 175° C. under a steam pressure of 6 to10 atm. The specific surface area is 105 m² /g.

U.S. Pat. No. 4,822,575 teaches a process for the preparation ofzirconium compositions which on calcination form zirconia. The zirconiumcompositions are prepared by the addition of an ammonia source to anaqueous zirconium sulfate solution to give a solution pH in the value offrom 0.1 to 2.5.

A general conclusion from the several disclosures is that up to now itwas very difficult to reach a higher specific surface area aftersintering of greater than 100 m² /g. In general the surface area was 80to 100 m² /g.

Now a process has been found that yields a convenient method for azirconia having a surface area of more than 125 m² /g after calcination,preferably more than 150 m² /g after calcination, more preferably morethan 200 m² /g after calcination.

SUMMARY OF THE INVENTION

The invention relates to a high surface area zirconia characterized by aspecific surface area of above 125 m² /g after calcination, preferablymore than 150 m² /g after calcination, more preferably more than 200 m²/g after calcination. The invention also relates to a high surface areazirconia characterized by a specific surface area of above 125 m² /gafter calcination, obtainable by mixing a zirconium salt solution withan alkali or ammonium compound, the precipitate being aged in thepresence of one or more oxygen acids of an element of group 5 or 6 ofthe Periodic Table of Elements, and subsequently being calcined,optionally after a washing step, the oxygen acid preferably beingphosphoric acid.

The invention also provides a process for producing high surface areazirconia products wherein zirconia is prepared from zirconium hydroxideby aging the zirconium hydroxide in the presence of an oxygen acid of anelement of group 5 or 6 of the Periodic Table of Elements andsubsequently calcining of at least 250° C., optionally after a washingstep.

BRIEF DESCRIPTION OF THE DRAWING

The sole drawing shows the effect aging zirconium hydroxide inphosphoric acid has on the surface area of the as calcined material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The instant zirconias are prepared by contacting a zirconium saltsolution with a solution of an alkali or ammonium compound to form aprecipitate of zirconium hydroxide. The precipitate is then aged in thepresence of one or more oxygen acids of an element of group V or VI ofthe Periodic Table of the Elements. The term "alkali compound" as usedherein refers to a compound that contains a hydroxy moiety or which uponhydrolysis with water generates hydroxyl ions. Thus, an alkali compoundis a compound capable of generating hydroxyl ions in the presence ofwater.

Calcination is suitably carried out at elevated temperature, e.g. morethan 250° C., preferably more than 300° C., more preferably more than350° C., still more preferably between 450° C. and 550° C., for a periodof at least 0.5 hour, preferably 1 to 4 hours, especially about 2 hours.The calcination is suitably carried out using an oxygen containing gas,especially air. Inert gases, e.g. nitrogen, helium, argon etc., may alsobe used.

Suitably, phosphor oxygen acids are used, especially orthophosphoric,metaphosphoric, hypophosphoric and pyrophosphoric acid. Preferablyorthophosphoric acid is used.

As a solvent preferably water is used, however, other polar solvents canbe used as well. Such as mixtures of water, ethanol, glycol and thelike.

The preferred alkali or ammonium compound is ammonia, preferably in a10% solution. Other alkali or ammonium compounds like for instance urea,hexamethylene tetraamine, (both generating hydroxyl ions by hydrolysis),ethanolamines, sodium and potassium hydroxide can be used too. In viewof the character of the alkali compounds additional washing steps arenecessary to wash the remainder out from the solids.

Preferably an aqueous 10% ammonia solution is used.

The zirconium hydroxide to be used in the process according to thepresent invention is suitably prepared by precipitating from a solutionof a zirconium compound in water by mixing with an alkali or ammoniumcompound, followed by filtration.

The product obtained by the filtration can be dried prior to sinteringalthough it is not strictly necessary. When it is dried before, careshould be taken that the drying is not too strong since that wouldaffect the properties of the product with regard to acid.

The preferred alkali is ammonia and the preferred aging time is 1/2 to 5hours, especially 0.8 to 1.2 hours. The precipitate suspension beingaged preferably in 0.8 to 1.2 molar in H₃ PO₄. The calcination ispreferably performed at 450° to 550° C.

The invention further provides a process for the production ofhydrocarbons from synthesis gas, characterized by using a catalyst on azirconia support obtained according to the present process, or,alternatively by using the zirconia as a catalyst itself, either is theform as described above, or mixed with other oxides, e.g. oxides ofmanganese, zinc, copper and/or chromium. The zirconia of the presentinvention may also very suitably be used in the so-called iso-synthesis.

An essential difference with the prior art zirconia is that theamorphous structure is substantially maintained during the calcination.Further it appeared that the acidity of the present material isconsiderably higher as appears from the adsorption of an excess ofammonia and increase of the temperature at which desorption is measured.

The present absorption is about three times the amount of ammonia andthe desorption occurs at 325° C. instead of 200° C. compared with priorart zirconia.

It further appeared that the aging time was of relative little influenceprovided that a certain minimum duration was obeyed. This minimum isabout half an hour. An effective aging time is 24 hours, longer agingtimes do not result in an increase of surface area. Suitably 1 to 4hours are used.

The ranges and limitations provided in the instant specification andclaims are those which are believed to particularly point out anddistinctly claim the instant invention. It is, however, understood thatother ranges and limitations that perform substantially the samefunction in substantially the same way to obtain the same orsubstantially the same result are intended to be within the scope of theinstant invention as defined by the instant specification and claims.

The invention will be described by the following examples which areprovided for illustrative purposes and are not to be construed aslimiting the invention.

EXAMPLE 1

1 Liter of 0.25M zirconia solution (produced by dissolving 66.10 g ofZrO(NO₃)₂.xH₂ O in demineralized water and diluting to 1 liter,resulting in an 0.25 molar solution) is brought into a glass reactorequipped with a double wall for temperature control and baffles toensure effective mixing. While stirring, 10% aqueous ammonia is addeddropwise at a rate of 1.35 ml/min. During the addition the pH valueincreases from 0.9 to 8.5. The solution is stirred for an other 0.5hours whereby the pH value decreases to 8.4. The precipitate is filteredoff and washed three times with 1 liter of demineralized water bysuspending the precipitate again and filtering it.

Subsequently 109.4 g of the wet precipitate of LOI=90.62% is suspendedin 100 ml of 0.25 molar H₃ PO₄ solution and stirred for 24 hours. Thematerial is then filtered off and washed on the filter with water. Thesolids obtained are dried at 120° C.

EXAMPLE 2

The process of example 1 is followed. After that the precipitate isobtained and has been washed and filtered 109.4 g of the wet materialhaving a LOI=90.62% is suspended in 100 ml of 0.5 molar H₃ PO₄ solutionand is stirred for 24 hours. The solid material is filtered off andwashed on the filter with demineralized water. The solids are dried at120° C.

EXAMPLE 3

Following the method of example 1, the pH value during the ammoniaaddition increases to 8.6. After 0.5 hours of stirring the pH valuedecreases to 8.5. The precipitate is filtered off and washed three timeswith 1 liter of demineralized water by suspending the precipitate againand filtering off. Then 116.12 g of the wet material having an LOI=88.7%is suspended in 100 ml of 1 molar H₃ PO₄ solution and stirred for 24hours. The material is filtered off and washed on the filter withdemineralized water. The solids obtained are dried at 120° C.

EXAMPLE 4

A zirconyl nitrate solution is produced by dissolving 71.04 g ofzirconyl nitrate in demineralized water, the solution being diluted withdemineralized water to 1 liter. This results into a 0.25M zirconiumsolution.

750 ml Of the zirconium solution are introduced in the 1 liter reactorand 50.0 g of urea are added.

Whilst stirring the solution is heated to 90° C. in about 1.5 hours.During the temperature increase the pH value decreases from 2.2 to 1.0and increases then slowly. After about 16 hours the pH stronglyincreases to 6.5 (final pH value). After 24 hours the experiment isstopped. The precipitate is filtered off and washed three times withdemineralized water by suspending the precipitate again in demineralizedwater and filtering it off. The solids are dried at 120° C. Evaluationof the products obtained.

The products obtained according to examples 1 to 4 are evaluated byheating the products for 1 hour on the temperatures indicated. Theproduct of each example was heated at 150°, 300°, 400° and 500° C. Theresults are indicated in the figure, curve A indicates the product ofexample 4, curve B indicates the product of example 1, curve C indicatesthe product of example 2 and curve D indicates the product of example 3.

As is readily apparent, the aging under influence of phosphoric acidresults into a considerably better surface area of the zirconia onaging.

What is claimed is:
 1. A process for producing zirconia having aspecific surface area of above 200 m² /g, which comprises precipitatingzirconium hydroxide from a solution of a zirconium compound in water bymixing said solution with an alkali compound selected from the groupconsisting of ammonia, urea, hexamethylene tetramine, ethanolamines,sodium hydroxide, and potassium hydroxide, washing the precipitate ofzirconium hydroxide with water to remove alkali compound therefrom,aging the washed precipitate in the presence of a phosphoric acid, andsubsequently calcining the aged precipitate at a temperature of about250° to 550° C.
 2. The process of claim 1 wherein the phosphoric acid isselected from the group consisting of orthophosphoric acid,metaphosphoric acid, hypophosphoric acid, pyrophosphoric acid andmixtures thereof.
 3. The process of claim 2 wherein the phosphoric acidis orthophosphoric acid.
 4. The process of claim 1 wherein the zirconiumhydroxide is prepared by precipitating from a zirconyl or zirconium saltor ammonium zirconium carbonate solution in water.
 5. The process ofclaim 1 wherein ammonia is used as alkali compound.
 6. The process ofclaim 1 wherein the zirconium hydroxide is aged for 1/4 to 5 hours at 0°to 100° C.
 7. The process of claim 6 wherein the zirconium hydroxide isaged for 0.8 to 1.2 hours.
 8. The process of claim 1 wherein thezirconium hydroxide is aged in 0.5 to 2 molar of acid.
 9. The process ofclaim 1 wherein the calcining is performed at a temperature of above300° C.
 10. The process of claim 9 wherein the calcining is performed ata temperature of 450° to 550° C.